It gets its power supply from the amplifiers power supply. I'm sure there would have to be load dropping resistors from the main supply in order to power this unit. Not the best Velleman kit to choose in my opinion. Velleman has another one with its own 6 volt supply on board and it is a much better piece.

There are those here that will argue that they hear a difference between a signal going thru a relay as opposed to going straight to the speaker. I do not hear any such difference.

While your system is much more primitave than other more expensive sounding systems there is still a need to try to guard against any damage that might rear its ugly head.

I think it probably uses any DC offset present to power the relay.
Don't you just connect it in series with the speaker. It should have no audible effect in practice, and although it's not the ideal way it has to be better than nothing.
Regards Karl

I don't think so... It would take a heap of DC offset to power the relay.

Go with the 4700 and make the modifications.

Hi, had a look on the Velleman web site, No extra PSU needed, uses the DC offset to operate the relay, that's why I said it was less than ideal, but there you go. I don't know what minimum voltage is needed to trip it
Regards Karl